I recently added a new bicycle tire to my gear, set it as default for cycling, but my new activities did not change the number of activities or mileage for the new tire. Garmin Connect is allocating the gear to the activity, but is not updating the mileage or activity count for the gear item. This can be corrected by removing the gear from the ride then adding it again, but that is a pain. I use the gear feature to track maintenance schedules for all of my parts that can wear out. Please fix this.
After some additional digging, it seems Garmin Connect stopped updating the gear statistics on or about September 4, 2018.